Change object representation from 1 big union to individual structs.

A big change.  Micro Python objects are allocated as individual structs
with the first element being a pointer to the type information (which
is itself an object).  This scheme follows CPython.  Much more flexible,
not necessarily slower, uses same heap memory, and can allocate objects
statically.

Also change name prefix, from py_ to mp_ (mp for Micro Python).
diff --git a/py/emitcpy.c b/py/emitcpy.c
index cb8bef4..52f8049 100644
--- a/py/emitcpy.c
+++ b/py/emitcpy.c
@@ -6,12 +6,12 @@
 #include <assert.h>
 
 #include "misc.h"
-#include "mpyconfig.h"
+#include "mpconfig.h"
 #include "lexer.h"
 #include "parse.h"
 #include "compile.h"
 #include "scope.h"
-#include "runtime.h"
+#include "runtime0.h"
 #include "emit.h"
 
 #if MICROPY_EMIT_CPYTHON
@@ -136,9 +136,9 @@
     if (emit->pass == PASS_3) {
         printf("LOAD_CONST ");
         switch (tok) {
-            case PY_TOKEN_KW_FALSE: printf("False"); break;
-            case PY_TOKEN_KW_NONE: printf("None"); break;
-            case PY_TOKEN_KW_TRUE: printf("True"); break;
+            case MP_TOKEN_KW_FALSE: printf("False"); break;
+            case MP_TOKEN_KW_NONE: printf("None"); break;
+            case MP_TOKEN_KW_TRUE: printf("True"); break;
             default: printf("?=%d\n", tok); return; assert(0);
         }
         printf("\n");